Helical primary structures of 1,3-spiroannelated five-membered rings: (±)-trispiro[4.1.1.4.2.2]heptadecane and (±)-tetraspiro[4.1.1.1.4.2.2.2]heneicosane

A combination of three spiroannelation methods forms the basis for a synthesis of the first two helical hydrocarbons of 1,3-spiroannelated five-membered rings.